1. Field of the Invention
This invention relates to a resealable, easy open container wall, such as a can end and, more specifically, it relates to a unique closure composition for use in such container walls.
2. Description of the Prior Art
The prior art teaches various structures for containers such as drawn and ironed cans having end panels which have integral opening devices which are generally called "easy open ends" double seamed to the can. Examples of easy open ends of the prior art are described in U.S. Pat. Nos. 3,929,251; 3,977,341; 3,997,076; 4,024,981; and 4,148,410.
The market for containers having easy open ends may be extended, particularly, though not exclusively, with respect to containers having larger capacities. This may be accomplished through the utilization of a cap to close and reseal the spout or pouring opening defined by the easy open end prior to discharge of all of the contents. Without a resealable closure cap, the liquid contents of an open container could easily spill or otherwise be lost. Also, dissociable gases, i.e., carbonation, in the remaining liquid are readily lost from unsealed, open containers, thereby altering the character of the product.
One construction for a resealable closure cap assembly is taught in U.S. Pat. No. 4,580,692. See also U.S. Pat. Nos. 4,685,849 and 4,783,985. These patents teach constructions for such a resealable closure cap assembly in association with a selectively contoured can end to accommodate the resealable closure while retaining the advantages characteristic of the easy open end. These patents disclose a sealing cap having a seal portion, an arm for securement to the container wall by means such as a rivet and a tab for use in grasping the cap to move it from one position to another. The cap is generally circular and has the arm emerging therefrom at a position generally about 90 degrees offset from the place where the tab projects outwardly.
United States patent application Ser. No. 338,096, filed on Apr. 14, 1989, discloses venting of such a resealing cap during removal of the resealing cap from the container so as to resist undesired reverse displacement of the container wall end panel which would establish a potentially serious hazard. This application discloses the use of venting channels which are transversely located in an inwardly directed ledge of the closure. See generally U.S. Pat. No. 4,928,844.
U.S. Pat. No. 4,932,555 discloses such a system which creates zones of weakness between the cap and the rivet securing the arm connecting the cap with the rivet.
United States patent application Ser. No. 338,310, filed Apr. 14, 1989, is directed toward such a system wherein improvements are provided to the container wall spout.
United States patent application Ser. No. 338,580, filed Apr. 17, 1989, discloses a releasable fastening assembly in the form of an additional projection from the cap which is adapted to cooperate with a button-like member formed in a container wall to resist undesired rotation of the cap.
United States patent application Ser. No. 397,218, filed Aug. 23, 1989, discloses the use of a plurality of stiffening ribs in such a reclosure cap so as to provide zones of different elasticity from other zones. It also discloses the absence of such ribs in the region connecting the arm which secures the cap to the container and the remainder of the cap. It also contemplates the possible omission of ribs from the region adjacent to the arm in order to provide for venting in this region.
The disclosures of all of these United States patents and co-pending United States patent applications are expressly incorporated herein by reference.
The provision of commercially acceptable resealable easy open can end constructions for current and larger volume beverage containers requires ease of application of the resealing cap over the spout, sealed retention of remaining container contents and accommodation of inherent internal can pressure that builds after resealing the can. Also desired is a can end configuration having an easy open can end which does not require the use of lever mechanisms or the like to accomplish opening of the pouring spout. Ideally, the easy open end is easily and readily opened by a user through the mere application of digital pressure in a simple and safe manner. Such construction of a resealable easy open can end should be accomplished without diminution of the convenience and cost effective nature of the basic easy open end construction during manufacturing, filling, handling, shipping, distributing, selling and consumer usage.
Experience to date with resealable caps and can end constructions, such as those disclosed in U.S. Pat. Nos. 4,580,692 and 4,648,528, the disclosures of which are incorporated herein by reference, has indicted a need to assure proper application and retention of the resealable cap over the spout defined by the easy open end.
In United States patent application Ser. No. 601,453, filed Oct. 22, 1990, entitled "Venting Resealable Container Closure Container Combination," the disclosure of which is expressly incorporated herein by reference, a unique self-venting construction for reclosure caps for pressurized containers is disclosed. In that invention the closure is so designed that if the internal container pressure exceeds a predetermined upper limit a portion or portions of the closure will be unseated so as to vent the excess pressure and will automatically reseat itself. In order to provide optimum performance of the invention disclosed in this application it is desirable to have a closure material having a number of unique properties.
It has been known to improve the characteristics of polyethylene film by blending polyethylene with other materials to enhance certain properties. See, generally, U.S. Pat. Nos. 2,434,662 and 2,499,756.
The use of anti-blocking agents to resist undesired blocking in polyethylene films has been known. See U.S. Pat. Nos. 2,770,608, 3,021,296 and 3,969,304.
It has also been known to blend polyethylene with waxes, such as paraffin wax or microcrystalline wax. See, generally, U.S. Pat. Nos. 2,504,270, 4,130,618 and 4,632,955.
U.S Pat. No. 2,615,857 discloses a gel of polyethylene and polyisobutylene employed in potting electrical components. The preferred composition contains about 71/2% polyethylene and 92% polyisobutylene.
It has been known to use polyethylene materials in packaging. U.S. Pat. No. 2,577,816 discloses a mixture of paraffin wax, polyisobutylene and polyethylene to form a strong blocking resistant, waterproof coating for paper. U.S. Pat. No. 2,238,681 discloses screw closures and crown closures having ethylene polymer cushion lining having a crystalline structure. It also teaches employing modifying agents such as paraffin wax.
U.S. Pat. No. 4,885,352 is directed toward low density polyethylene plastic extruded film of the type used in wrapping and displaying foods that are to be refrigerated. It also discloses the use of a large number of possible additives for increasing the cling properties of the polyethylene film. Among the suggested cling additives are polyisobutylene.
One of the problems with caps having self-venting capabilities employed to reclose containers of pressured liquids is the need to have a material that will withstand a variety of conditions. For example, an opened container left in the hot sun or placed horizontally must be capable of venting increased pressure while resisting undesired spillage.
In spite of the prior art disclosures, there remains a very real and substantial need for a material having the unique properties required for a reclosure for container walls having a weakened zone which is adapted to fracture and create an opening which will be reclosed by cap of this invention.